The present invention relates to a mechanism for positioning a transducing head in a disc drive system, and more particularly relates to a piezoelectric microactuator integrated into an actuator arm of a disc drive system to provide high resolution head positioning over a selected track of a rotatable disc.
Concentric data tracks of information are being recorded on discs with increasing track densities, which reduces the margin for error in positioning a transducing head over a selected track due to the reduced radial distance between tracks and the narrow radial width of the tracks themselves. Typical actuator motors lack sufficient resolution to accurately position a head in a system implementing a disc with a high track recording density.
Various proposals have been made to provide a second, high resolution motor, or microactuator, to finely position a head at a radial position over a track, in addition to the low resolution actuator motor. These "dual-stage actuation" systems have taken a variety of forms. Some of the proposed designs would install a microactuator in the head slider itself. These designs require significant changes in the manufacturing of head sliders. A solution that allows existing mass manufacturing techniques for sliders to be used would be more desirable. Other proposed designs would replace a conventional gimbal with a specially designed silicon gimbal having a microactuator formed directly on the gimbal itself. Again, these designs require news complex gimbal manufacturing techniques, which are less efficient than a solution that utilizes existing disc drive components. Still other proposed designs would mount a microactuator motor where the actuator arm meets the head suspension. While these designs often require only minimal changes in the actuator arm head suspension designs, the connection between the actuator arm and the head suspension must be carefully designed to include the microactuator motor. In addition, none of the proposed designs includes a microactuator having the capability of sensing a position of the head slider based on a state of the microactuator. A solution with this capability, that requires minimal additional design steps to conventional actuator assembly design, would be a significant improvement over the presently proposed dual-stage actuation systems.
The present invention is directed to a piezoelectric microactuator embedded in the actuator arm of a disc drive system. U.S. Pat. No. 4,814,908 to Schmitz discloses a system for radially positioning a transducing head over the center of a track on a rotatable disc by placing a thermal element on one side of the actuator arm. The arm is made of a material which expands upon heating and contracts upon cooling, so that the arm can be expanded or contracted (thereby radially moving the transducing head carried by the arm) in response to controlled heating or cooling of the thermal element. However, the thermal element has a relatively slow response time, making it inadequate for some high performance disc drive systems. Also, expansion of the thermal element in response to a given input stimulus is not sufficiently precise and predictable to serve as an effective high resolution positioning mechanism. The introduction of heat into the actuator arm affects the environmental conditions of the disc drive, which can have significant effects on the operation of the positioning system. Finally, the current state of a thermal element cannot be readily detected, making it difficult to determine the appropriate input stimulus to effect incremental transformation of the microactuator to precisely position the head over a selected track.